The present invention relates generally to a method and apparatus for sorptively storing a multiconstituent gas, such as an odorized natural gas or other multiconstituent gaseous fuel, in a storage vessel having a sorbent material therein. More particularly, the present invention relates to such a method and apparatus for substantially preserving a relative concentration of at least one of the constituents of the multiconstituent gas at a predetermined minimum concentration level relative to other constituents of the multiconstituent gas, both before and after sorptive storage in the storage vessel. It should be noted that the terms "sorbent" and "sorptive", and the like, as used herein, refer to the use of either an adsorbent or an absorbent material.
Recently, in gaseous fuel storage applications, as well as from other gas storage applications, it has been found that the use of high-surface-area sorptive materials (adsorbents or absorbents) has provided for significantly increased storage capacities of such gases at relatively low pressures. This has led to the development of various vehicular and non-vehicular applications of gaseous fuels for both portable and non-portable gaseous fuel consuming devices. Examples of such applications are disclosed and discussed in more detail in U.S. Pat. Nos. 4,531,558; 4,523,548; 4,522,159, and No. 4,776,366 (issued Oct. 11, 1988), all of which are assigned to the same assignee as the present invention, and the disclosures of which are hereby incorporated by reference herein.
While the above-mentioned systems and apparatuses for gaseous fuel storage have proved to be highly advantageous, the use of sorbent materials for such storage frequently results in the removal of odorants or other desirable additives or constituents that have been included in such gaseous fuels for safety purposes or for other reasons deemed necessary or desirable in a particular application. Such undesirable removal of odorant additives or other desirable constituents of a multiconstituent gas typically results from the fact that such odorants, additives, or other desirable constituents frequently include heavier, longer-chain compounds that are preferentially sorbed (absorbed or adsorbed) by the sorbent material relative to the other constituents of the gaseous fuel or other gas. Consequently, although such preferentially sorbed materials are present in the gaseous fuel or other gas in predetermined minimum desirable concentrations in the gas supplied to the storage apparatus, the preferential sorption of these materials in the storage tank or vessel causes them to be substantially removed, or at least reduced to undesirably low levels, when the stored gas is removed from the storage vessel for use.
The need has thus arisen for a sorptive gas storage apparatus and method wherein predetermined minimum quantities or concentrations of certain preferentially sorbed additives or constituents of a multiconstituent gas are substantially preserved at minimum concentration levels, both before and after the multiconstituent gas is sorptively stored in the storage vessel.
In accordance with the present invention, a method and apparatus is provided for sorptively storing a multiconstituent gas in, and for selectively releasing the multiconstituent gas from, a vessel having a predetermined sorbent material therein, while substantially preserving minimum quantities or concentrations of certain constituents of the gas. In such a method and apparatus, a first of the constituents of the multiconstituent gas, which is preferentially sorbed by the predetermined sorbent material, is present in the multiconstituent gas in a predetermined minimum quantity or concentration level substantially less than the quantity of the second constituent. First, the sorbent material in the vessel is sorptively saturated with a pre-storage quantity of the first constituent at a first predetermined pressure. Then the multiconstituent gas to be stored is introduced under pressure into the vessel, with the vessel being pressurized to a second predetermined pressure that is higher than the above-mentioned first predetermined pressure. This causes both of the first and second constituents of the multiconstituent gas to be sorptively stored in the vessel on the sorbent material therein.
When the stored and pressurized multiconstituent gas is selectively released from the vessel, the sorbent material therein desorptively releases the multiconstituent gas, with the first constituent being present in at least the above-mentioned predetermined quantity or concentration, as the pressure in the vessel decreases during the desorptive release of the stored gas. Effectively, because of the pre-storage saturation of the sorbent material with the desired first constituent at a first predetermined pressure level, the desired concentration level of such preferentially-sorbed first constituent is substantially preserved in the stored multiconstituent gas being withdrawn from the storage vessel for use in a gas-consuming system or other application.
In one preferred embodiment of the invention, the above-mentioned first predetermined pressure, at which the sorbent material is sorptively saturated, is approximately equal to atmospheric pressure, but other pressures may also be desired in particular applications. Thus, when the multiconstituent gas is introduced into the storage vessel for sorptive storage therein, it is pressurized to a second predetermined pressure higher than the preferred atmospheric first predetermined pressure. Preferably, the pre-storage quantity of the first constituent is introduced into the sorbent material for sorptive saturation in a gaseous state. However, because such first constituents frequently have vapor pressures lower than the first predetermined saturation pressure, such constituents can alternatively be introduced in a liquid state, with the sorbent material sorptively retaining the first constituent in a gaseous state.
Also, in the preferred form of the invention, the sorbent material is sorptively saturated in the manner described above after the sorbent material is placed in the storage vessel. Alternatively, however, if deemed necessary or desirable in a particular application, such sorptive saturation can be performed prior to the sorbent material being placed in, or otherwise associated with, the storage vessel.
Additional objectives, advantages, and features of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings.